Method of distillation of tar



Jan. 2, 1934. J M w 5 1,942,195

METHOD OF DI STILLATION OF TAR Original Filed Sept. 30, 1926 INVENTOR. 21% 7 v 105% A TTORN E S.

55 still and thereby avoiding loss of oil vapors.

Patented Jan. 2, 1934 PATENT OFFICE I 1,942,195 I METHOD or DISTILLATION F TAR John Morris Weiss, New York, N. Y., assignor,

by mesne assignments, to The Barrett Company, New York, N. Y., a corporation of New Jersey Application September 30, 1926, Serial No. 138,582 Renewed November 8, 1930 3 Claims.

This invention relates to improvements in the process of distilling tar, especially tar obtained by the destructive distillation of coal or the pyrogenetic decompositon of petroleum oils. One

5 object of the invention is to carry on the distillation in a smooth, even fashion and avoid the deposition of carbon on the shell of the still. Another object is to increase the distillate yield from a tar to a certain melting point pitch. A

13 further object is to obtain higher melting point pitches than can be obtained in the ordinary methods of distillation. In addition there are other features of the invention, for example, a more convenient method of light oil recovery 15 which will be evident as the description proceeds.

The term tar as used in this specification is intended to include all varieties of coal tar, carburetted water gas tar, oil gas tar, blast furnace tar, ligrite tar, etc. In the distillation go of these tars, the greater the formation of free carbon, the less the yield of distillate oil and the greater the residual pitch. As oil has a higher market value than pitch, it is advantageous to produce as high a yield of oil as possible. For this reason vacuum distillation has been used with good effect but applying this to the ordinary tar still involves constructional changes to safeguard against external pressures at high temperatures and the degree of vacuum necessary for best results is difficult, if not impossible, to

maintain in practical operations. When the tar temperatures reach a certain point it is impossible to maintain a high vacuum owing to the evolution of uncondensible gases from the decomposition of the tar, unless a pump of such over capacity is used as to render the installation uneconomical.

In my United States Patent No. 1,418,893 filed February '7, 1920 and issued June 6, 1922, I dis- 40 closed the facts that air normally used for agitating the tar during distillation tended to decrease the oil yield and that by the use of a gas chemically inert to the tar as an agitating means during the distillation and by using the gas in sufficient amount to appreciably lower the vapor pressure of the oils distilling, that the distillation could be accomplished at lower temperatures, with less cracking and therefore materially higher yields of oil than in the prior batch still processes.

As the amount of oil carried by the gas was cona natural result the light oils were partly condensed with the heavy oils and would have required a redistillation of the heavier oils if it were necessary to completely separate them.

I have now discovered a way in which this disadvantage can be obviated, when the geographical location of the tar distillation plant is favorable and these light oils recovered without redistilling the heavier oils or put to useful work without recovery as such. Coal tar is produced at gas works andby-product coke oven plants and gas is always obtained along with the tar in the carbonization of coal. In the gas works the gas is used for domestic heating and illuminating purposes and is usually mixed with water gas which is carburetted by cracking petroleum oil and thereby adding to the water gas hydrocarbons of high calorific value thereby raising it to the standard set by the particular regulatory body under whose jurisdiction the gas company is operating. In the coke oven plants, the gas is usually used for fuel purposes within the plant but before being so used for fuel it is scrubbed with a suitable oil to recover its content of benzol and other low boiling hydrocarbons. In the present invention I take gas after the tar has been separated from it but not necessarily further purified and pass it through the tar still during distillation to provide agitation and reduce the vapor pressures and thereby the distilling temperature of the tar vapors to the desired extent. The distillate is condensed and the gas separates from the condensed liquid naturally carrying some of the tar light oils in uncondensed form. This gas is then allowed to return to the main gas make of the plant. In the case of the gas works these added light oils will serve as a valuable enriching agent and enable the plant to use less carburetting on their water gas set, thereby saving both material and fuel. In the coke oven plant or other plant with similar facilities, the gas goes to oil scrubbers where the tar light oil would be removed along with the other light oil in the gas, in this way being obtained in a suitable form for refining and at a convenient point from the standpoint of operation. As the tar light oil is of the same general nature as the light oil in the gas, there is no interference with routine scrubbing practice or the subsequent refining operations.

As illustrative of how the process can be applied to tar distillation, reference may be made to the appended drawing which is purely diagrammatic but it must be understood that I denser V which in turn delivers to a receiver VI provided with a drawoff VII, a vent VIII and an outlet pipe IX. This line delivers into a main gas line of the plant X. Gas may be drawn from this main or another suitable gas source through the pipe XI and is forced by the pump XII through the gas preheater XIII and by the pipe XIV to the bottom of the interior of the still through the perforated pipe XV. Arrows are used to indicate the direction of gas flow.

The still is charged with the tar to be dis? tilled, the system closed and heat applied. Gas is p ssed t r h stil at the d si d it w th o ith ut rehe ih D s illation ts an se ht hhe w h as Pa sa u til th due in the st ll is oi the de i ed eehs s ehey he vela il r du s ei -is arried i tem t til w th h a a for th mas a ein ond n ed in the ehiie se V d eq e ed n h receiver VI- Th as s ll he siihe som poi"-- tien of th ta 0.11s l a e th re e r by the pipe IX and is returned to the gas line of the ant an for x mple! in e eek e e o e tion, goes to oil scrubbers where the tar Va.- nersso c ri d ar recov r al ne i h the light oils normally in the gas. When the distillation is fin shed hea hd ha s ag are i e h timed a d the s u r meveq f om the i l- I Pi te t a s an am un of sas e s them 1 cu it at rdin r atm sp er res r and te atu e and n t e ha 20 u fter min e erlleh f tee et s a ch ed in the st ll Br heatihe he s as e i de i a b t ec s ary- I con id r my nteeess .ih ht e t f the i r e s st l h ed, he type of se n h eth f e ing, the type of or means of cooling the condenser, th m an used f me ihe t e as t The yields of oil by my process will in the ease of coke oven coal tars, when distilled to itshes e a mel in int 9f a ou d 0 be from 10 to 18% higher than when the same tars are distilled without gas passage. A further advantage of the process over ordinary batch still operation is that the residue may be run to a much higher melting point without endangering the apparatus or coking the charge and pitches of a melting point above 300 F. up to at least 450 F. can be obtained when this process is used without difficulty or undue coke formation on the shell of the still. The light oil in the gas is recovered if so desired or may be left there to increase its enriching power.

In the claims where the term fuel gas is used, Iintend to include coal gas, water gas, oil gas and the like.

Having thus described my invention I claim:

1, The process of distilling tar with the aid of fuel gases, which comprises diverting part of a main stream of fuel gases, passing the gases so diverted through hot tar contained in a still to promote distillation of the tar, cooling the resulting gases and vapors to condense oils therefrom, and returning the gases and uncondensed tar vapors thus cooled to the main stream of the fuel gases subsequent to the point from which the gases were diverted.

2.- T e im ro m i he process o aim 1, in which the fuel gases are tar laden gases and which are freed of their tar before introducing them into t e still, a d in which the m tr am of fuel gases, together with the'gases employed for tar distillation, after re-cornbination, are passed to an absorbing system to recover light oils therefrom.

3, The process of distilling tar with the aid 1 ef fuel gases, which comprises generating fuel gases containing tar constituents, cooling the gases and separating condensable constituents therefrom, dividing the gases into two streams, pas the stre m h ou t tar contained in a still to promote distillation thereof, c-ooling the resulting gases and vapors to condense gils therefrom, returning the gases and uncone densed vapors, after such cooling, to the other hert h of h as s a a ng t e om ined gas streams to an absorption system for recovery M or ight il t re m JOHN MORRIS WEISS. 

